The present invention relates generally to electronic ballasts for gas discharge lamps.
More particularly, this invention pertains to an electronic ballast that includes end of lamp life protection, overheating protection, automatic shut-down protection capabilities, reignition capabilities, and multiple striking capabilities.
Electronic ballasts for gas discharge lamps are well known in the art and include a variety of different types of protection features and capabilities. For example, the prior art includes electronic ballasts that include end of lamp life protection circuits that are designed to protect the electronic ballast and the gas discharge lamp from being damaged by an end of lamp life condition. The prior art includes electronic ballasts having overheating protection circuits that are designed to protect a ballast from being damaged by excessive heating conditions. The prior art also includes electronic ballasts that include reignition circuits that are designed to automatically ignite a gas discharge lamp when it is reconnected to the electronic ballast. In addition, the prior art includes electronic ballasts that include multiple striking circuits that are designed to generate multiple striking attempts that can be used to ignite cold, new, or old gas discharge lamps that can be difficult to ignite with an otherwise single strike.
An end of lamp life condition is a condition that occurs when a gas discharge lamp reaches the end of its effective operating lifetime. When this occurs, as an instance, the gas discharge lamp can begin to rectify the AC current applied to the gas discharge lamp. The gas discharge lamp can rectify current in a positive direction, commonly referred to as positive rectification, or in a negative direction, generally referred to as negative rectification. Regardless of the direction of rectification, the rectification causes the peak to peak voltage across the gas discharge lamp to gradually increase and, as a result, the power drawn by the gas discharge lamp and thus the ballast. This is an undesirable condition because the ballast is usually very sensitive to the increased power it has to deliver to the lamp and it will be overheated and eventually destroyed by this increased power. Similarly, this situation can cause damage to the gas discharge lamp. In addition, an end of lamp life condition can also cause the peak to peak voltage across the gas discharge lamp to increase symmetrically. Once again, the increasing voltage causes the power drawn by the gas discharge lamp and thus the ballast to increase and this can damage both the electronic ballast and the gas discharge lamp.
The end of lamp life protection circuits in the prior art are designed to sense an end of lamp life condition in a gas discharge lamp and to compensate for this condition before the electronic ballast or the gas discharge lamp can be damaged by the various end of lamp life conditions that can occur. Typically, the protection circuits are designed to command the electronic ballast to simply shut down completely. Alternatively, the protection circuits can cause the electronic ballast to reduce the power delivered to the gas discharge lamp to a safe level that will not damage the electronic ballast or the gas discharge lamp.
An overheating condition typically occurs when consumers improperly install electronic ballasts in areas where they cannot be properly cooled. As a result, these electronic ballasts overheat and eventually fail, resulting in customer dissatisfaction and increased customer costs. Overheating protection circuits are designed to sense and compensate for this type of condition before the electronic ballast or the gas discharge lamp can be damaged by excessive heat. As was the case with end of lamp life protection circuits, overheating protection circuits may command an electronic ballast to shut down completely or to reduce the power delivered to the gas discharge lamp to a safe level so that the ballast will not be damaged by excessive heat.
Examples of electronic ballasts including end of lamp life protection circuits, overheating protection circuits, automatic reignition circuits, and multiple striking circuits are described in U.S. Pat. No. 6,420,838, issued to Shackle on Jul. 26, 2002 and entitled “Fluorescent lamp ballast with integrated circuit,” U.S. Pat. No. 6,366,032, issued to Allison, et al. on Apr. 2, 2002 and entitled “Fluorescent lamp ballast with integrated circuit,” and U.S. Pat. No. 5,925,990, issued to Crouse et al. on Jul. 20, 1999 and entitled “Microprocessor controlled electronic ballast.”
Although the prior art does appear to teach several different types of a protection circuits for electronic ballasts, these circuits have several disadvantages. For example, end of lamp life protection circuits taught by the prior art must be designed to handle very high currents and, as a result, dissipate large amounts of power. This makes these types of protection circuits fairly inefficient. In addition, many prior art end of lamp life protection circuits sense DC rectification end of lamp life conditions or excessively high AC end of lamp life conditions, but not both. Known overheating protection circuits suffer from an inability to accurately sense when an overheating condition has occurred and, consequently, do not provide adequate overheating protection. Prior art reignition circuits can inadvertently attempt to reignite a lamp load even after a ballast has been shut down by another protection circuit.
In addition to the above-referenced disadvantages of prior art protection circuits, the applicant has also recognized that the prior art does not appear to teach one protection circuit that includes all of the desired protection and capabilities described above in an inexpensive, simple but reliable package. While prior art electronic ballasts do include end of lamp life protection circuits, overheating protection circuits, reignition circuits, multiple striking circuits, or some combination of these features, many of these prior art ballasts require expensive microprocessors or complicated circuits including a large number of component parts to accomplish each protection feature separately, both of which are very undesirable from the consumer and the manufacturer viewpoint.
What is needed, then, is an electronic ballast that includes end of lamp life protection, overheating protection, reignition capabilities, and multiple striking capabilities in an inexpensive, simple package and that overcomes the disadvantages of prior art electronic ballasts.